Hello David,
We’re always glad to hear that our product is making your work easier! 
Regarding the term “expression,” I believe you’re referring to the one below:
iif(@CustTrans_markForPaymentSchedule != "" and data-source('Parameters')/@PrintPaymentSchedule = "false", "true", "false")
Let me explain this expression in plain language:
So, this expression will give a “true” result if these two conditions are met:
- When @CustTrans_markForPaymentSchedule is not empty or blank, and at the same time,
- @PrintPaymentSchedule (which comes from the Parameters data source) has a value of “false.”
Please note that if you’ve selected the Inverted check mark, the operation will work oppositely. In this case, the “If” tagging will hide the content instead of displaying it, or vice versa. That being said, the line needs to have some value for payment schedule but print payment schedule needs to be false to be shown.
For the second section @ISOpenTransaction: The field needs to have a value “false” indicating that it is closed which will show the fields under that If tagging element to be shown.
The @IsOpenTransaction can either have “true” or “false” value (never both), which will hide the lines that are in “open” (@IsOpenTransaction = "true") state.